In a network device such as hub, switch controller, Network Interface Card (NIC), etc., a physical layer device for transmitting and/or receiving signals is required.
Conventionally, when there are idle periods interspersed between data packet transmission, normal idles are continuously transmitted or link pulses are intermittently sent, for example as disclosed in U.S. Pat. No. 6,795,450 B1 issued to Mills et al. (see FIG. 5; numeral references 520 and 530 indicate normal idles and link pulses, respectively), which is incorporated herein for reference. As suggested by Miller et al., power consumption during normal idle state or non-link suspend is continuously kept at a certain level. On the other hand, the power consumption between link suspend pulses can be minimized.
Ethernet switch controller, which is an example of a network device, including a plurality of physical layer devices can simultaneously provide a plurality of ports for connecting to cables. When the interface transmission rates between two network devices are different, e.g. the interface transmission rates may vary from 10 BASE-T (100 MHz) to 100 BASE-T (100 MHz) and further to 1000 BASE-T (GHz), a link pulse such as a normal link pulse or a fast link pulse can be used for networking. After link proceeds, both network devices utilize a proper encoded signal, e.g. MLT-3, to perform a differential transmission.
Although Ethernet switch controller provides a plurality of ports for connecting to cables, some of the ports may be in an unused status. That is, corresponding physical layer devices of some ports may be unlinked or dumbly link without data transmission therebetween. However, these corresponding physical layer devices still keep outputting the link pulses to inform the remote network device. For example, as shown in FIG. 1, the unused physical layer devices keep outputting a link pulse of 100 ns in width every 16±8 ms. Furthermore, because the transmission signal is transmitted in a differential transmission manner, the physical layer devices, even in an unused status, also consume significant common mode bias current.
Therefore, the present invention discloses how to save electrical power for a physical layer device and a new physical layer device structure to deal with the above situations encountered in the prior art.